The invention concerns a light beam position detector with a detection window, for detecting a position of a striking light beam within the detection window, which detection window comprises a first PSD based on the lateral photoelectric effect, in particular with two output signals dependent on the striking position of the light beam, and an electronic readout circuitry for the PSD. The detection window further comprises at least a second PSD based on the lateral photoelectric effect, being aligned in a geometrical line in succession with the first PSD, so that the first and the at least second PSD define the detection window.